Conventionally, a drill is known in which a groove is formed on the distal end face of the main body of the drill, an insert is attached to the groove in a detachable manner, and the insert after having been used is thrown away without resharpening, so that resharpening processes for tools are omitted, and the time for changing tools is reduced. Such a technology in drills is disclosed, for example, in Japanese Unexamined Patent Application, First Publication No. H11-197923. In the drill disclosed in this document, an attachment hole having a circular hole shape is formed on a bottom face of a groove that is directed to a distal end, and an insert is provided with a cylindrical shank portion at a back face thereof that faces the bottom face. The insert is attached to the drill main body by inserting the shank portion into the attachment hole. The shank portion has a notch, and an engagement element is provided inside the attachment hole; therefore, the engagement element engages the notch when the shank portion is inserted into the attachment hole, and thus the insert is fixed to the drill main body.
In the above-mentioned drill, because the insert can be fixed to the drill main body just by inserting the shank portion into the attachment hole, the process of attaching the insert is simplified, and thus efficiency is obtained; however, a problem is encountered in that the shank portion may be broken if it is too thin since the connection between the insert and the drill main body is achieved by the shank portion. Moreover, aligning (centering) of the insert with respect to the drill main body is achieved only by the engagement of the shank portion with the attachment hole; therefore, the aligning accuracy may be insufficient, which may lead to degradation in machining accuracy of the drill with respect to a workpiece.
In addition, when a workpiece is machined by a drill, in general, machining oil is supplied during the machining process. For this, conventionally, as shown in FIG. 11, a flow path 102 is formed in a drill main body 100 so as to extend in the direction of an axis O of the drill main body 100, branched paths 103 are branched in two directions from the flow path 102 at a distal portion thereof, the branched paths 103 are connected to openings 104 which are formed in a distal end face 107 of the drill main body 100, and machining oil is provided in a machining oil supply section 105 which is connected to the proximal end of the flow path 102 so that machining oil is supplied between the workpiece and an insert 101 via the flow path 102, branched paths 103, and openings 104. However, because the branched paths 103 are formed in the distal portion of the drill main body 100, the strength of the distal portion, which is made thinner and weakened by a groove 106, is further decreased due to the branched paths 103; therefore, another problem is encountered in that the distal portion of the drill main body 100 may deform outwardly so as to be away from the groove 106, as shown in FIG. 12. Furthermore, the formation of the branched paths 103 necessitates a greater number of manufacturing processes and more complicated manufacturing processes.